The present invention relates generally to self-propelled mowers and, more specifically, to mowers with electric drives, particularly robotic or autonomous mowers.
Robotic or autonomous residential lawn mowers are often battery powered and include an electric drive for the blade as well as for the wheels. An example of such a mower is the commercially available Friendly Robotics model RL500. The run times of such mowers are severely limited by the relatively high energy requirements which quickly drain the on-board batteries. The cutting device on the mower is a principle source of energy drain. Rotating blades with wing surfaces to create air flow for moving grass clippings and the impacting of the blades against the grass during cutting and/or mulching consume large amounts of power. For example, a single mower blade can require from a half to five horsepower, and a typical battery pack often has a maximum output of one horsepower or less. Therefore, severe limitations must be placed on blade design and blade function to lessen power requirements, and such limitations often reduce mower capacity and the ability of the mower to mow, mulch and move clippings. Even with the imposed limitations, premature failure of the electric motor driving the blade is common as a result of the heavy loading and severe operating conditions encountered by the mower. Available mower run times are relatively short, and recharging the batteries on such a mower can take up to twelve hours or more and require access to an electrical outlet.
Hybrid mowers, an example of which is shown in U.S. Pat. No. 6,044,922 issued to Bruce F. Field, include both an engine and a source of electrical power but typically provide electric drive to the cutting element. The drive wheels are either driven directly from the engine as disclosed in the above Field patent or by one or more electric motors, such as shown in U.S. Pat. No. 6,082,084 issued to Kirk W. Reimers et al. Therefore, although more power can be directed to the electric blade driving motor and run times can be extended by driving an alternator with the engine to maintain battery charge, the blade horsepower requirements and electric blade motor life expectancy still dictate blade design and function limitations that result in less than optimum mowing performance. Further, in robotic or autonomous mowers any use of direct engine-to-wheel drive such as shown in the Reimers patent, or in U.S. Pat. No. 5,528,888 issued to Yasuhiko Miyamoto et al, can require costly and complicated drive and steering controls.
It is therefore an object of the present invention to provide an improved drive system for a self-propelled mower. It is another object to provide such a system which overcomes most or all of the aforementioned problems. It is still a further object to provide such a drive system which is particularly useful with a robotic or autonomous mower.
It is another object of the present invention to provide an improved drive system for a self-propelled mower having an electrically powered motor wherein blade performance is substantially improved compared to at least most previously available mower systems with electric drives. It is another object to provide such a system which improves mower capacity and run times and shortens turn-around times for improved mower productivity.
It is a further object of the present invention to provide an improved self-propelled mower having an electric wheel drive system in combination with an engine-driven blade drive which overcomes the blade design limitations typical of at least most previously available mower systems with electric drives. It is another object to provide such a system which obviates problems of electric drive cutter blades while retaining the control advantages present in an electric wheel drive system. It is yet a further object to provide such a system which is particularly useful with robotic or autonomous mowers.
In accordance with the above and additional objects of the invention, a self-propelled mower is provided with an internal combustion engine directly driving blade structure, including a single or multiple cutter blades such as winged mower blades, a reel or multiple reels. Drive is through a direct connection to the main drive shaft of the engine, a belt-type drive powered by the engine, or a hydrostatic drive having a pump connected to the engine and hydrostatic motor structure connected to the mower blades or reels. A source of electrical power on the mower includes a battery pack connected to a generating device such as an alternator connected to the engine. Drive structure supports the mower for movement over the ground and preferably includes drive wheels connected to electric motor structure powered exclusively by the source of electrical power. A controller connected to a navigation system and to the electric motor structure selectively powers the drive structure from the source to control mower speed and direction.
The drive system is particularly useful with autonomous and robotic mowers. Mower propulsion and steering is directed by the navigation system and controller. Cutting devices with higher power requirements and better cutting and conveying capacity, such as the winged blades or multiple reels, can be used since limitations of electric motor drives are avoided. Mower wheel drive is never directly coupled to the engine but is connected to the electrical power source so that speed, direction and steering control is less costly and complex than in other types of propulsion systems, including hybrid systems, connecting the engine more directly to the wheels. Run time and mower capacity is significantly increased compared to at least most mowers having battery packs without on-board generating capability. The mower engine can be run at an optimum speed for maximizing engine efficiency and mower capacity while the electrical system provides precise control of torque, speed and direction. Complicated and costly transmission structure is avoided.
These and other objects, features and advantages of the present invention will become apparent to one skilled in the art upon reading the following detailed description in view of the drawings.